High brightness light emitting diode (LED) light sources are in high demand for challenging applications in machine vision. Prior art in the machine vision lighting field typically utilize tungsten or tungsten halogen, metal halide, and xenon arc lamps or, more recently, systems incorporating pre-packaged high brightness LEDs. High intensity linear lighting is used to illuminate the field of view of line scan cameras to visualize objects including printed materials on high speed printers and a variety of manufactured products that travel by on a moving conveyor belt or platform for what is typically referred to as web inspection. High performance, low cost, compact, and reliable linear lighting is desirable for such tasks.
Until recently, tungsten halogen lamps typically coupled into glass fiber optic bundles arranged in a line and imaged to a line by use of a spherical cylindrical lens was the industry standard. Companies such as Schott Fiber Optics, Dolan Jenner, Volpi, Illumination Technology, and Fiberoptic Technology manufacture such products with a range of available intensities and line lengths. For example, a single twenty four inch long linear lighting system from Schott Fiber Optics, the recognized industry leader, is comprised of two separate tungsten halogen light boxes coupled to two one half inch glass fiber optic cables which, in turn, terminate into a single twenty four inch long length of fiber which images to the illumination plane by use of a cylindrical spherical rod lens. With a new tungsten halogen 150 Watt EKE Lamp, this system yields a maximum of approximately one million Lux (lumens per square meter). One of the most serious limitations of tungsten halogen technology is that the intensity of the lamps degrades at a fast rate. At full power, tungsten halogen lamps last only between about 50 hours and 500 hours before their initial intensity has degraded by the order of 50%, or the lamps fail by filament burn out. The cost of the lamps is not the primary concern, however. It is the cost of shutting down a line to replace the lamp that is primarily driving the need for LED based systems.
Consequently, it is a primary object of the present invention to provide a highly reliable line source of illumination suitable for use in a variety of applications.
It is another object of the present invention to provide a linear line source utilizing LEDs.
It is yet another object of the present invention to provide a high intensity linear line source for use in machine vision applications.
Other objects of the invention will be obvious and others will appear hereinafter when the following detailed description is read in connection with the accompanying drawings.